This invention relates to a filter housing and pleated filter for the filtration of particulate matter from fluids, particularly air.
There are many known filters that use a fibrous nonwoven filter media that is pleated into a zigzag shape. This shape of filter media is desirable in terms of providing good filter efficiency and loading capacity in a relatively small cross-sectional area.
The structural integrity of the pleated filter's zigzag shape is typically provided by a rigidifying member other than the filter material. For example, U.S. Pat. No. 3,793,813 discusses the use of a cardboard frame in which is included the fibrous filter material. Also employed in the art are wire supports, such as discussed in U.S. Pat. No. 3,853,529 and polymeric rigidifying materials which are disclosed, for example, in U.S. Pat. Nos. 5,376,218, 5,240,479 and 5,306,321 and PCT Application No. 93/11849. With the possible exception of thicker wire mesh support, generally these rigidifying elements are not sufficiently rigid at the bending lines to maintain the pleat spacing of the filter material and additional external supports are required. A common approach is to adhesively secure the side edges of the pleated filter to the sidewalls of a rigid filter frame, such as disclosed in U.S. Pat. Nos. 5,397,632 and 5,098,767. However, there have been proposals to maintain pleat spacing by other methods including adhesive beads placed on the strip along the tops of the pleat structures as disclosed in U.S. Pat. No. 3,692,184 and a bead of adhesive, such as disclosed in U.S. Pat. No. 3,397,518.
In U.S. Pat. No. 5,306,321 pleat spacing is maintained by forming indents at the tops of the pleated filter which indents form "Pleatloc" dimples. These dimples contact each other and thereby prevent the pleated filter faces from coming into full contact and also maintain pleat spacing.
In U.S. Pat. No. 5,167,740 the pleat spacing of a zigzag filter is maintained by placing the filter material, along with any polymeric rigidifying netting, into a jig with a portion of thermoplastic filter material and netting extending beyond the jig. This extended filter and netting material is then swiped with a heated platen while in the jig. This fuses the thermoplastic filter material and netting forming a rigid continuous side panel of the fused thermoplastic material. As the fused side panel is still continuously connected to the pleated filter material the pleat spacing of the filter material is locked in place.
Mechanical means for maintaining pleat spacing include zigzag teeth-type elements. In U.S. Pat. No. 3,793,813, two zigzag shaped ribs are placed along two opposing sidewalls of a filter housing. The rigid pleated filter, in a cardboard frame, sits on these ribs so that the ribs maintain the pleat spacing of the filter. In U.S. Pat. No. 4,547,950, two tapered combs are placed on the downstream face of a pleated filter where the teeth of the combs extend partially into the upstream pleat structures. The teeth of the combs space the pleats on one face of the zigzag filter. The airflow presses the filter media against the teeth on the opposite face thereby maintaining the pleat spacing on that face. In both of the above patents the filter media would be pressed into the teeth valleys by the oncoming air stream. A problem with this approach is that the filter media can easily fall out if not restrained on the opposite face when not in use (i.e., during production, installation, shipping, etc.).
In other U.S. patents, instead of teeth-type support structures on only one face of the pleated filter, two interengaging teeth structures are used. These interengaging teeth are on opposite faces of the pleated filter thereby clamping the zigzag shaped filter media between the opposing teeth elements, such as disclosed in U.S. Pat. Nos. 2,058,669, 4,177,050 and 3,873,288. This avoids problems with the filter media falling out, however, filter media performance is lost where the opposing teeth elements engage. In the first two patents, multiple interengaging teeth elements are placed along the central body portion of the filter housing, although in the '050 patent the opposing teeth do not fully engage. This is to avoid overly compressing the filter medium to minimize loss of filter performance. In U.S. Pat. No. 3,873,288 the opposing interengaging teeth fully compress the filter medium between the engaging teeth elements, however, the teeth elements also form the housing and as such, the teeth only peripherally engage and compress the filter medium.